Kelly's Heroes is a good movie. It's got one hell of a cast. Telly Savalas Don Rickles Carroll O'Connor Donald Sutherland Don Rickles in a WW2 movie. How could it possibly not be awesome?
Two very good movies. My friend says Absolute Power is good too but I haven't seen it so I don't know. Costner has some good movies...Waterworld (well, I liked it), Open Range, Wyatt Earp, Dances With Wolves (of course)
It shocks me that no one has mentioned Space Cowboy as that has one of the best casts ever in Clint Eastwood, Donald Sutherland, James Garner, and Tommy Lee Jones. If that's not a cast just full of win then I don't know what is. I would also like to second (or third) Kelly's Heros and Letters From Iwo Jima. Oh and I would recomend seeing the rest of The Man With No Name trilogy (Fist Full of Dollers, and For a Few Dollers More) and Hang'em High.
Well he's done so many good ones, if you havent watched the Dollars Trilogy you should, I watched High Plains Drifter this weekend which he also directed and was good, the first 4 in the Dirty Harry series are(Dead Pool sucked), In the Line of Fire, Unforgiven, Every Which Way but Loose and Any Which Way you Can if you like corny unserious fun movies, basically any western he's done is pretty good, can't really go wrong there.